All U.S. patents cited below are herein entirely incorporated by reference.
As used herein, the term “thermoplastic” is intended to mean a polymeric material that will melt upon exposure to sufficient heat but will retain its solidified state, but not prior shape without use of a mold or like article, upon sufficient cooling. Specifically, as well, such a term is intended solely to encompass polymers meeting such a broad definition that also exhibit either crystalline or semi-crystalline morphology upon cooling after melt-formation through the use of the aforementioned mold or like article. Particular types of polymers contemplated within such a definition include, without limitation, polyolefins (such as polyethylene, polypropylene, polybutylene, and any combination thereof), polyamides (such as nylon), polyurethanes, polyester (such as polyethylene terephthalate), and the like (as well as any combinations thereof).
Thermoplastics have been utilized in a variety of end-use applications, including storage containers, medical devices, food packages, plastic tubes and pipes, shelving units, and the like. Such base compositions, however, must exhibit certain physical characteristics in order to permit widespread use. Specifically within polyolefins, for example, uniformity in arrangement of crystals upon crystallization is a necessity to provide an effective, durable, and versatile polyolefin article. In order to achieve such desirable physical properties, it has been known that certain compounds and compositions provide nucleation sites for polyolefin crystal growth during molding or fabrication. Generally, compositions containing such nucleating compounds crystallize at a much faster rate than un-nucleated polyolefin. Such crystallization at higher temperatures results in reduced fabrication cycle times and a variety of improvements in physical properties, such as, as one example, stiffness.
Such compounds and compositions that provide faster and or higher polymer crystallization temperatures are thus popularly known as nucleators. Such compounds are, as their name suggests, utilized to provide nucleation sites for crystal growth during cooling of a thermoplastic molten formulation. Generally, the presence of such nucleation sites results in a larger number of smaller crystals. As a result of the smaller crystals formed therein, clarification of the target thermoplastic may also be achieved, although excellent clarity is not always a result. The smaller crystal size, the less light is scattered. In such a manner, the clarity of the thermoplastic article itself can be improved. Thus, thermoplastic nucleator compounds are very important to the thermoplastic industry in order to provide enhanced clarity, physical properties and/or faster processing.
The most effective thermoplastic nucleator in terms of high crystallization temperatures is a saturated bicyclic dicarboxylate salt available from Milliken & Company under the tradename of HPN-68, disclosed within U.S. Pat. Nos. 6,465,551 and 6,534,574, both entirely incorporated herein by reference, along with other like saturated dicarboxylate salt nucleator compounds (HPN-68 itself is disodium bicyclo[2.2.1]heptanedicarboxylate). Other measurable physical improvements such compound types impart to thermoplastics include greater stiffness and superior dimensional stability. Thus, at least in standard additive introduction processes for thermoplastic production, the utilization of saturated bicyclic dicarboxylate salt nucleators can ultimately result in improved part quality and/or faster production cycle times as compared with other nucleators.
Other thermoplastic nucleating agents that exhibit appreciably lower crystallization temperatures, as well as less effective dimensional stability levels, etc., as compared with saturated dicarboxylate salt types, include dibenzylidene sorbitol compounds, such as 1,3-O-2,4-bis(3,4-dimethylbenzylidene)sorbitol (hereinafter DMDBS), available from Milliken & Company under the trade name Millad® 3988, sodium benzoate, sodium 2,2′-methylene-bis-(4,6-di-tert-butylphenyl)phosphate (from Asahi Denka Kogyo K.K., known as NA-11), talc, cyclic bis-phenol phosphates (such as NA-21, also available from Asahi Denka), and, as taught within Patent Cooperation Treaty Application WO 98/29494, to Minnesota Mining and Manufacturing, the unsaturated compound of disodium bicyclo[2.2.1]heptene dicarboxylate. Such compounds all impart relatively high polyolefin crystallization temperatures; however, each also exhibits its own drawback for large-scale industrial applications, and none can match the effectiveness of the above-noted saturated types.
Some of the above-noted nucleating agents also provide clarifying properties within certain thermoplastics, such as polypropylene (Millad® 3988, for example, and to a lesser extent, NA-21). Such clarification capabilities coupled with high peak crystallization temperatures are highly desired. The previously listed dicarboxylate salt nucleating agents unfortunately generally exhibit relatively high haze levels within polypropylene, although such compounds also provide excellent calcium stearate compatibility and increased stiffness within target thermoplastic articles. Thus, such compounds provide extremely desirable qualities and benefits within target thermoplastics. Unfortunately, as noted above, in certain applications haze issues have limited the usefulness of saturated bicyclic dicarboxylate nucleating agents, even though the crystallization temperatures imparted thereby are extremely high.
Also limiting the widespread utilization of such bicyclic dicarboxylate salt nucleators is the lack of providing proper concentrates (i.e., masterbatches) of such additives within thermoplastic production methods. Concentrates of thermoplastic additives are highly desirable for a number of reasons. Generally, the primary purpose for these concentrates has been to provide the end-use manufacturer with the flexibility to impart a wide variety of desirable properties to both general and specific purpose plastic polymers. Such concentrates contain any number of different types of additives, such as, as merely examples, organic and inorganic colorants, inorganic fillers, antioxidants, lubricants, acid scavengers, etc., and have been utilized for many years within the plastics industry. Thus, such concentrates provide a highly effective delivery system of additives in order to impart any number of different properties to the subject, ultimate thermoplastic formulation and/or article. These imparted properties may include lubricity, protection from oxidation, protection from UV degradation, protection from corrosion, antimicrobial protection, clarity, opacity, nucleation, antiblocking performance, antistatic performance, flame retardancy, viscosity change, organoleptic enhancements, impact improvement, increased stiffness, improved dimensional stability, color, and enhancements to other optical, physical, and rheological properties. Unless a plastic polymer producer or a custom compounder has the economic justification to provide a pre-compounded polymer system having the desired properties requested by a particular end-use manufacturer, then the use of concentrates is required by the end-use manufacturer to meet market demands as these manufacturers (i.e. injection molders, compression molders, extruders of film, sheet, pipe, etc., thermoformers, blow molders, rotational molders, etc.) do not typically have the means or economic incentive to produce customized resins for their own consumption. As a result, concentrates that are both efficient and cost-effective provide the greatest value to the thermoplastic end-use manufacturer.
Unfortunately, to date, effective concentrates of saturated bicyclic dicarboxylate salt nucleating additives have not been forthcoming. Past methods of introduction within thermoplastic manufacturing procedures have basically been limited to utilization of the powder or granule form of such nucleators directly within a thermoplastic formulation and/or stream prior to melt-compounding, extrusion, molding, etc., and thus added in an amount that is at-level with the amount present within the finished article (such as, without limitation, 1500 ppm), and subsequent cooling. As alluded to above, the utilization of powders complicates manufacturing methods and makes transport and introduction relatively difficult for the user. Thus, concentrates (materials when primarily comprised of carrier polymer and relatively high amounts of a nucleator that, when admixed and melt-blended with target polymer resins, permit subsequent let-down of a relatively low amount of the desired concentrate within such a target resin or finished article thereof)(a/k/a/, masterbatches)(such terms are well understood by the ordinarily skilled artisan within such the thermoplastics industry) are highly regarded for dispensing and storage. Again, however, such masterbatches or concentrates have been difficult to provide for these highly desired nucleating additives to date. The mere incorporation of such concentrated nucleators within pellets of polypropylene (or other like polymer) has not translated into effective high peak crystallization temperatures within the ultimate end-use article. Hence, there is a need to develop proper concentrate formulations in order to permit proper utilization of such bicyclic dicarboxylate salt nucleators without sacrificing the benefits such additives impart to subject thermoplastics. Unfortunately, there have been no concentrates available that have provided an economically attractive route to obtain optimum nucleation performance, along with the associated improvements of stiffness and dimensional stability, as well as potentially better clarity. This invention is thus directed to such an achievement.